I never knot and bury them until the quilting is done and the quilt is off the frame, because I find sometimes there is a loop, knot or slack on the backside of the quilt, which needs to be dealt with before the ends are knotted, buried and cut. I wish I could do them as I go, because sometimes it's a bit overwhelming to do all at once at the end, not to mention anticlimatic. I recently had 11 hours spent knotting and burying threads on a custom quilt---not even my own!! Not my favorite thing to do......